Vacuum canister size 80 series and prado

[flyology]

I have just upgraded the brakes on my 60 series to Surf/4runner front calipers (4x45mm pistons on each caliper) I also up graded to an 80 series dual diaphragm booster, 80 master cylinder and have converted the rear drums to disc.

brakes are great on the first application, but on hitting them a couple of times they pedal gets very hard as if the booster is not working, or I am running out of vacuum to operate the booster. I can't hear any leaks when its running and when turn off there is still vacuum in the booster (checked by pulling the hose off)

What size vacuum canister do 80 series and prados (they have dual diaphragm booster also) have?

I am running the standard 60 series canister, wondering if it is too small??

Any ideas?

thanks,

MB